Recently, a display device using a mechanical shutter to which a MEMS (Micro Electronic Mechanical Systems) technology is applied (hereinafter, such a shutter will be referred to as a “MEMS shutter”) has been a target of attention. Such a display device (hereinafter, referred to as a “MEMS display device”) opens or closes a MEMS shutter provided in correspondence with each of pixels, at a high speed by use of a TFT, to control the amount of light to be transmitted through the shutter, and thus adjusts the brightness of an image (see, for example, Japanese Laid-Open Patent Publication No. 2008-197668). A mainstream gray scale system of such MEMS display devices is a time-ratio gray scale system of displaying an image by sequentially switching light provided from one of LED backlight units of red, green and blue to light provided from another of the LED backlight units. Accordingly, the MEMS display devices have features that polarizing films or color filters used for a liquid crystal display device are not required; and as compared with a liquid crystal display device, the utilization factor of backlight is about 10 times higher, the power consumption is no more than half, and the color reproducibility is superior.
A MEMS display device is formed as follows. A TFT including switching elements for driving MEMS shutters, and gate and data drivers for driving the switching elements is formed on a substrate. Terminals for supplying signals from an external device to the TFT are also formed on the substrate. Usually for forming a MEMS display device, on the TFT substrate having the TFTs and the terminals formed thereon, a passivation film (insulating film) for covering the TFTs and the terminals is formed, and MEMS shutters are formed on the passivation film. An insulating film is formed to cover the MEMS shutters except for a part of each MEMS shutter which is to be electrically connected to a terminal. A movable section of the MEMS shutter has a hollow structure. Therefore, the insulating film is formed by CVD (Chemical Vapor Deposition) or the like on the entirety of a surface of the TFT substrate having the MEMS shutters formed thereon, so that a side surface and a bottom surface of the movable section is covered with the insulating film. Then, a counter substrate is joined to the TFT substrate. The terminals formed on the TFT substrate need to be supplied with signals from an external device. Therefore, the TFT substrate and the counter substrate are joined together such that the counter substrate does not cover a top surface of each terminal.
In order to supply signals and electric power to the terminals formed on the TFT substrate from an external device, the insulating film on the terminals needs to be removed to expose the terminals. The insulating film can be removed by, for example, a combination of a photolithography process and an etching process. However, the insulating film provided as the passivation film (lower-layer insulating film) and the insulating film provided on the lower-layer insulating film for covering the MEMS shutter (the insulating film provided on the lower-layer insulating film will be referred to as the upper-layer insulating film) are often both formed of a nitride film, which has splendid properties as a covering film and as an insulating film. Therefore, it is difficult to perform etching such that only the upper-layer insulating film is removed and the lower-layer insulating film is left having a sufficient thickness. When etching proceeds to the lower-layer insulating film, lines formed on the TFT substrate may be exposed, which may undesirably cause insulation failure or continuity failure.
The present invention made in light of the above-described problems has an object of providing a display device and a method for producing the same for removing an insulating film from top of terminals while suppressing the thickness reduction of an insulating film provided for protecting a surface of a TFT substrate and thus improving the reliability of the TFT substrate.